Involvement of nitric oxide in pioglitazone memory improvement in morphine-induced memory impaired mice

Introduction

Pioglitazone, a PPAR‐γ agonist, which is clinically used in treating diabetic patients, has been recently reported to have crucial roles in improving cognition and memory performance. Since the mechanisms involved in the neuroprotective effect of pioglitazone are not entirely understood, the current study was designed to investigate the possible interaction of pioglitazone with morphine in memory-impaired mice and the probable role of nitric oxide (NO) in this effect.

Materials and methods

All the experiments were performed in passive avoidance and Y-maze paradigms. To induce memory impairment, mice were administered morphine (1, 3 and 10 mg/kg, s.c.) immediately before the training trial. Pioglitazone (20, 40 and 80 mg/kg, p.o.) was gavaged 2 h prior to the training trial. Further, an NO synthase inhibitor, L-NAME (10 mg/kg, i.p.), or an inducible NO synthase inhibitor, aminoguanidine (100 mg/kg, i.p.) was administered 30 min before the training trial to determine the possible involvement of NO in the restorative effect of pioglitazone.

Results

1) Morphine dose dependently impaired the acquisition of spatial memory and passive avoidance task. 2) Treatment with pioglitazone significantly improved the memory performance in morphine-treated mice in both tests. 3) In the passive avoidance task, L-NAME, but not aminoguanidine, altered the effect of pioglitazone on morphine-induced memory impairment. 4) In Y-maze discrimination, the memory improving effect of pioglitazone was reversed by both NO synthase inhibitors, L-NAME and aminoguanidine.

Discussion

Our results demonstrate that the pioglitazone improving effect on the morphine-induced impairment of memory acquisition is at least in part through the NO pathway. It is suggested that in short term spatial recognition memory, both inducible and constitutive NO synthases are involved, but in the long term fear memory, only the constitutive NO synthases indicated a prominent role in the anti‐amnestic effect of pioglitazone on morphine-induced memory impairment.     

一氧化氮合酶抑制剂对七叶莲花镇痛作用的影响

目的 探讨一氧化氮合酶(NOS)抑制剂与七叶莲花镇痛作用的关系. 方法 采用小鼠热板法,将小鼠随机分为等渗盐水组(阴性对照组)、曲马多组(阳性对照组)及各实验组,观察L-精氨酸(L-Arg)和NOS抑制剂L-硝基精氨酸甲酯(L-NAME)对七叶莲花醇提物(SAHF)镇痛作用的影响. 结果 与等渗盐水组比较,L-NAME可显著增强七叶莲花的镇痛作用(P<0.01);与SAHF组比较,脑组织中NO水平显著降低(P<0.05). 结论 七叶莲花的镇痛作用和NOS抑制剂之间存在一定的相互作用,L-NAME可显著增强七叶莲花的镇痛作用,提示SAHF的镇痛作用机制与降低体内过量的NO有关.     

Different effects of dexamethasone and the nitric oxide synthase inhibitor L-NAME on caerulein-induced rat acute pancreatitis, depending on the severity

Effects of dexamethasone and N^G-nitro-L-arginine methyl ester (L-NAME), the nitric oxide (NO) synthase inhibitor, on caerulein-induced acute pancreatitis were examined in rats. Acute pancreatitis was induced by caerulein (20 μg/kg, s.c.) given repeatedly 2 or 4 times every hour, and serum amylase levels, pancreas weight and myeloperoxidase (MPO) activity were measured 6 h after the first injection of caerulein. Dexamethasone (3 mg/kg) and L-NAME (30 mg/kg) were administered p.o. 30 min before the first injection of caerulein. Caerulein caused moderate or severe pancreatitis, depending on the times of injections, resulting in different degrees of increase in serum amylase levels and pancreas weight, and the marked elevation of MPO activity was observed only after injections of caerulein given 4 times per hour. Both dexamethasone and L-NAME suppressed the severity of pancreatits, yet the effect of L-NAME as compared with dexamethasone was more potent against mild pancreatitis but less potent against severe pancreatitis. These results suggest that caerulein-induced acute pancreatitis shows different responsiveness to L-NAME and dexamethasone, depending on the severity; the former is more effective against pancreatitis with less inflammation, while the latter is more effective against pancreatitis with severe inflammation. It is assumed that endogenous NO may be involved in oedema formation as the early event in the development of acute pancreatitis.     

Comparative effects of selective and non-selective nitric oxide synthase inhibition in gentamicin-induced rat nephrotoxicity

Different nitric oxide synthase (NOS) isoforms are found in the kidney. Some studies provided evidences that increased endothelial NOS (eNOS) activity leads to restoration of renal function after injury, but activation of inducible NOS (iNOS) aggravates renal failure. In the present study, the beneficial effects of selective iNOS blockade in gentamicin (GM) induced nephrotoxicity have been investigated. Four groups of rats were studied. Untreated control rats received saline. In GM group, GM was injected (IV, 4 mg kg⁻¹). In GM + L-NAME group rats received L-NAME (N-omega-l-arginine methyl ester, a non-selective NOS inhibitor) simultaneously with GM (IV, 30 mg kg⁻¹). Additional doses of L-NAME were administered 2 and 4 h after GM (IP, 30 mg kg⁻¹). In GM + L-NIL group rats were treated by N-imino-ethyl lysine (L-NIL, a selective iNOS inhibitor). First dose (IV, 3 mg kg⁻¹) administrated simultaneously with GM. Next doses (IP, 3 mg kg⁻¹) were administered 2 and 4 h after GM. In all groups, serum and urine creatinine levels were measured. Creatinine clearance was calculated and considered as an estimation of glomerular filtration rate (GFR). Urine N-acetyl-b-d-glucose aminidase (NAG) activities were also determined. After experiments, kidney sections were histologically studied. Selective iNOS inhibition by L-NIL prevented the GM-induced decrease in GFR and increase in creatinine levels, while complete non-selective NOS inhibition by L-NAME aggravated the GFR reduction, elevation of creatinine levels and enzyme release (P < 0.05). Histological studies showed that GM-treated kidneys had evidences of tubular damages and these damages were less evident by the administration of L-NIL. In conclusion, selective inhibition of iNOS may prevent GM-induced nephrotoxicity, whereas non-selective inhibition of NOS aggravates it.     

Effects of nitric oxide synthase inhibitors on the discriminative stimulus effects of cocaine in rats

RATIONALE: Nitric oxide synthase (NOS) inhibitors may modulate the discriminative stimulus effects of cocaine because they alter dopamine (DA) release. OBJECTIVES: The effects of the NOS inhibitors NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitro-indazole (7-NI) were examined in experiments designed to better understand the mechanisms that may underlie the interactions between NOS inhibitors and cocaine. METHODS: Rats were trained to discriminate 10 mg/kg cocaine from saline, and then substitution and pretreatment tests with L-NAME and 7-NI were conducted. To determine if the combined effects of NOS inhibitors and cocaine might be related to DA mechanisms and/or to N-methyl-D-aspartate (NMDA) receptor mechanisms, substitution tests with other indirect DA agonists and NMDA antagonists were carried out in the presence and absence of L-NAME. In addition, the roles of the D1 and D2 families of DA receptors in mediating the cocaine-altering effects of L-NAME and 7-NI were examined in antagonism tests using SCH 23390 and haloperidol, respectively. RESULTS: The results demonstrated that neither NOS inhibitor alone substituted for the 10 mg/kg cocaine training dose, but when given as a pretreatment, 100 mg/kg L-NAME as well as 10 mg/kg 7-NI enhanced the discriminative stimulus and rate-decreasing effects of cocaine. L-NAME pretreatment also enhanced the potency of (+)-amphetamine and GBR 12909, but not MK-801, phencyclidine, or NPC 17742, for producing discriminative stimulus and rate-decreasing effects in substitution tests. Further testing showed that the cocaine-enhancing effects of L-NAME and 7-NI were attenuated by doses of haloperidol and SCH 23390 that minimally altered the effects of cocaine alone. CONCLUSIONS: These findings suggest that L-NAME and 7-NI may increase the potency of cocaine and other indirect DA agonists through a central mechanism whereby DA neurotransmission is directly enhanced by NOS inhibition.     

依普拉芬对去卵巢大鼠血清一氧化氮及一氧化氮合酶的影响

目的探讨人工合成的植物雌激素依普拉芬对去卵巢大鼠血清一氧化氮及一氧化氮合酶合酶的影响。方法6个月龄雌性SD大鼠60只分为假手术组（10只SD大鼠）和去卵巢组（50只）;再将去卵巢大鼠分为阴性对照组,依普拉芬高、中、低剂量组和雌激素对照组（各10只）,分别给予基础饲料和不同剂量的依普拉芬,12周后测定血清NO及NOS。结果与假手术组相比,去卵巢大鼠阴性对照组血清NO及NOS明显降低,依普拉芬组高于阴性对照组,与假手术组比较差异无统计学意义。同时低于雌激素组。结论NO及NOS参与了骨质疏松的病理生理过程;依普拉芬可以通过提高去卵巢大鼠血清NO及NOS浓度达到防治绝经后骨质疏松症的作用。     

孕酮对东莨菪碱所致记忆损伤小鼠的作用及机制

目的观察孕酮对东莨菪碱所致记忆损伤小鼠的作用及机制。方法东莨菪碱(1mg·kg-1,ip)造成小鼠记忆损伤模型,利用被动逃避实验评价小鼠记忆成绩,并测定给药后24h小鼠皮质和海马胆碱酯酶(AChE)和胆碱乙酰转移酶(ChAT)的活性。结果在被动逃避实验中,东莨菪碱造成小鼠记忆损伤,孕酮(1、10mg·kg-1,sc)预处理能减少跳台错误次数(P<0.05),延长跳台潜伏期(P<0.01)和避暗潜伏期(P<0.01)。东莨菪碱增加皮质和海马AChE活性,降低ChAT活性,孕酮(1mg·kg-1,sc)预处理抑制皮质和海马AChE活性的增加(P<0.01),升高皮质(P<0.05)和海马(P<0.01)ChAT活性。结论孕酮可以改善东莨菪碱所致记忆损伤,机制可能与其抑制皮质和海马AChE活性、升高ChAT活性有关。     

Role of nitric oxide in the gastric cytoprotection induced by central vagal stimulation

The role of nitric oxide (NO) in the vagal cholinergic-mediated cytoprotective effect of intracisternal (i.c.) injection of the stable thyrotropin-releasing hormone (TRH) analog, RX 77368, was investigated in conscious rats. RX 77368 (1.5 ng i.c.) reduced by 88% gastric hemorrhagic lesions induced by oral administration of ethanol (60%). L-N^G-Nitro-arginine methyl ester (L-NAME, 3 mg/kg i.v.), an inhibitor of NO synthase, abolished the cytoprotection provided by i.c. RX 77368. The effect of L-NAME was reversed by L- but not D-arginine. These results suggest that the L-arginine-nitric oxide pathway is involved in the cytoprotective effect of i.c. TRH analog, probably through the modulation of gastric mucosal blood flow.     

Effects of the nitric oxide donor molsidomine on different memory components as assessed in the object-recognition task in the rat

RATIONALE: Nitric oxide (NO) is sought to be a novel intracellular messenger in the central nervous system. Recently, NO involvement in learning and memory processes has been proposed. Compounds that inhibit NO synthase, the key synthesizing enzyme, may block cognition, while NO donors may facilitate it. OBJECTIVES: The present study was designed to further investigate in the rat the effects on distinct memory processes exerted by the NO donor molsidomine. For this aim, the object-recognition task was chosen. This test is based on the differential exploration of a new and familiar object.METHODS. Object recognition was evaluated in a two-trial nonrewarded paradigm. In a first study, the influence of the retention time (the delay between the two trials) on the performance of 3-month-old male rats was assessed. Subsequently, the effects of molsidomine (2 mg/kg and 4 mg/kg), injected i.p., on acquisition, storage, and retrieval of information were evaluated. For the latter experiments, the delay condition at which recognition memory was extinguished in the normal rat was used (24 h). RESULTS: Under our experimental conditions, object recognition was extinguished in the rat when an intertrial interval (ITI) of 24 h was utilized. Using this ITI, molsidomine at 4 mg/kg but not at 2 mg/kg improved the animal's performance in the object-recognition task, suggesting that molsidomine affected acquisition, storage, and retrieval of information. CONCLUSIONS: These results indicate that the NO donor molsidomine may modulate different aspects of memory.     

Scavenging of hydroxyl radicals but not of peroxynitrite by inhibitors and substrates of nitric oxide synthases

1. The nitric oxide synthase inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) is widely used to study the role of NO^• in physiological and pathological processes, including its role in the generation of the cytotoxic species peroxynitrite (ONOO⁻) and of reactive oxygen radicals such as hydroxyl (OH^•). Often L-NAME is applied to tissues at mM concentrations. At such high concentrations, it might act as a free radical scavenger. A similar possibility might apply to the use of high levels of arginine to study the role of NO^. in atherogenesis.
2. We therefore examined the rate of scavenging of OH^• by L-NAME and found that L-NAME reacts more quickly with OH^. than the established ‘OH^. scavenger'' mannitol and the widely used `OH^• trap'' salicylate. However, D-NAME can scavenge OH^• at rates equal to L-NAME. Both L- and D-arginine were also good OH^• scavengers, comparable in effectiveness to mannitol.
3. Neither L-NAME, D-NAME, L-arginine nor D-arginine was able to inhibit ONOO⁻-dependent nitration of tyrosine, suggesting that they are unlikely to be scavengers of ONOO⁻-derived nitrating species.
4. Neither L-NAME, D-NAME, L-arginine nor D-arginine was able to inhibit the inactivation of α₁-antiproteinase by ONOO⁻, suggesting that they cannot prevent direct oxidations by peroxynitrite.
5. We conclude that L-NAME has sufficient activity as an OH^• scavenger to confound certain pharmacological experiments. However, this explanation of its biological effects can be ruled out if control experiments show that D-NAME has no effect and that L-arginine (also a free radical scavenger) antagonizes the action of L-NAME.

     

Motor effects of acute and chronic inhibition of nitric oxide synthesis in mice

RATIONALE: Systemic injections of nitric oxide synthase (NOS) inhibitors have been shown to decrease exploratory behavior in rats. This effect may be related to motor impairments since these drugs can induce catalepsy in rodents. OBJECTIVE: To compare the effects of two NOS inhibitors in tests aimed to investigate exploratory behavior and to assess motor control. METHODS: The acute effects of the NOS inhibitors NG-nitro- L-arginine ( L-NOARG, 10-80 mg/kg IP) and 7-nitroindazole (7-NIO, 3-30 mg/kg IP) on exploratory activity were analyzed in an open field arena. Drug effects on catalepsy were examined in the hanging-bar and wire-ring test. Footprint pattern after treatment with the two NOS inhibitors was evaluated and the results compared with those obtained with the dopamine D2 receptor antagonist haloperidol (1-2 mg/kg IP). Sub-chronic (twice a day for 4 days) effects of L-NOARG (40 mg/kg) or 7-NIO (30 mg/kg) were also tested in the open field arena and catalepsy test. RESULTS: L-NOARG and 7-NIO decreased locomotion and rearing in the open field arena. Both drugs induced catalepsy in the hanging-bar test but did not change footprint pattern. The cataleptic effect of L-NOARG in the hanging bar and wire-ring tests were highly correlated ( r=0.927). The exploratory and cataleptic effects of L-NOARG and 7-NIO provided evidence for tolerance after sub-chronic treatment. CONCLUSION: These results confirm that inhibition of neuronal NO formation induces impairment of exploratory behavior. This effect does not seem to involve aspects evaluated by footprint analysis, such as weight support, trunk stability and foot placement. They could, however, be related to drug-induced catalepsy.     

Influence of nitric oxide agents in the dorsal hippocampus of mice on anxiogenic-like effect induced by histamine

Histaminergic receptors and neuronal nitric oxide synthase (nNOS) are co-expressed at high levels in the hippocampal neurons and alter anxiety-like behaviors in rodents. Since the dorsal hippocampus may be involved in modulation of anxiety-like behaviors, the aim of the present study was to assess whether the nitric oxide (NO) system in the dorsal hippocampus affects anxiety-like behaviors induced by histaminergic agents in mice. The effects of the NO precursor, L-arginine and NOS inhibitor, L-nitro-amino-methyl-ester (L-NAME) on histamine, pyrilamine and ranitidine responses in elevated plus maze (E.P.M.) in mice were investigated. Intra-CA1 microinjection of histamine (9 μg/mouse) or H1 receptor antagonist, pyrilamine (3, 6 and 9 μg/mouse), but not H2 receptor antagonist, ranitidine decreased the percentage of open arm time (%OAT) and open arm entries (%OAE), without affecting locomotor activity, suggesting an anxiogenic-like response. Both L-arginine (0.4 and 0.8 μg/mouse) and L-NAME (40 ng/mouse) when injected into the dorsal hippocampus induced anxiety-like behaviors, but the drugs reversed the anxiogenic response induced by the effective dose of histamine (9 μg/mouse) or pyrilamine (9 μg/mouse). Our results also indicated that intra-CA1 administration of L-arginine and L-NAME, in the presence or absence of ranitidine, exerted an anxiogenic effect. The results may indicate a modulatory role for NO in the dorsal hippocampus in the anxiogenic-like response induced by histamine or pyrilamine.     

Lack of phencyclidine-induced effects in mice with reduced neuronal nitric oxide synthase

RATIONALE: Phencyclidine (PCP) is widely used as an animal model of schizophrenia, because in humans it can induce positive and negative symptoms associated with schizophrenia. PCP is an antagonist of N-methyl-D-aspartate receptors, which are associated with the nitric oxide (NO) system. OBJECTIVE AND METHODS: The primary objective was to determine whether neuronal NO synthase (nNOS) is involved in PCP-induced behaviours and neuronal activation, as measured by the expression of c-Fos. After characterizing a PCP mouse model (dose-response study, Experiment 1), we measured PCP-induced effects in mice treated with nNOS antisense oligodeoxynucleotides (AS-ODNs) (Experiment 2), and in nNOS knockout (nNOS-/-) mice (Experiment 3). RESULTS: PCP 5 mg/kg induced the maximum behavioural effects of all doses tested, consisting of hyperlocomotion, stereotyped turning behaviour, without the presence of ataxia. PCP also induced an increase in Fos-like immunoreactivity (Fos-LIR) in the frontal cortex, as well as in the midline limbic (thalamic and hypothalamic nuclei) areas. In the AS-ODN-treated mice, PCP induced less behaviour when compared to water-treated controls. In the nNOS-/- mice, PCP induced less behaviour and a decrease in Fos-LIR in the frontal cortex and midline limbic areas, when compared to wild-type littermate controls. CONCLUSIONS: Our findings suggest that the frontal cortex and midline thalamic brain regions are involved in PCP-induced effects in mice. Furthermore, we show that an intact nNOS system is necessary to obtain PCP-induced effects. This may implicate nNOS as a viable drug target in the treatment of schizophrenia.     

支气管哮喘患儿血内皮素-1和一氧化氮水平测定及临床意义

目的　探讨内皮素 1(Endothelia 1,ET 1)和—氧化氮 (nitrcoxide ,NO )在儿童哮喘发病机制中的作用。方法　对 40例支气管哮喘患儿和 40例正常儿童进行了血浆ET 1及血清NO水平检测。结果　哮喘急性期患儿血ET 1和NO明显高于缓解期 (P <0 0 1) ,缓解期ET 1和NO虽有所下降 ,但仍高于对照组(P <0 0 5)。结论　ET 1和NO水平与哮喘病情严重程度成正相关 ,是反映哮喘严重程度的良好指标     

Antagonism of nitrous oxide-induced anxiolytic-like behavior in the mouse light/dark exploration procedure by pharmacologic disruption of endogenous nitric oxide function

Rationale. Previous studies have shown the anxiolytic-like effects of nitrous oxide (N₂O) to be sensitive to antagonism by non-specific inhibitors of nitric oxide synthase (NOS). Objectives. The present study was conducted to demonstrate further the involvement of nitric oxide (NO) and ascertain whether a specific isoform of NOS is involved in N₂O-induced behavior in mice. Methods. Male NIH Swiss mice were tested in the light/dark exploration test to determine how N₂O-induced behavior was affected by the following pretreatments: the NO scavenger hemoglobin (Hb); the selective nNOS-inhibitor S-methyl-l-thiocitrulline (SMTC); the selective eNOS-inhibitor N(5)-(1-iminoethyl)-l-ornithine (l-NIO); and the selective iNOS-inhibitor 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT). Furthermore, NOS activity was assessed in the whole brain as well as five brain areas of N₂O- versus room air-exposed mice to determine the effects of N₂O on NOS activity. Results. The behavioral effects of N₂O in the light/dark exploration test were significantly attenuated following pretreatment with Hb (2.0 nmol, i.c.v.), SMTC (0.3 μg and 1.0 μg per mouse, i.c.v.) and the higher dose of l-NIO (30 mg/kg, s.c.). However, the N₂O-induced behavioral effect was unaltered by pretreatment with either the lower dose of l-NIO (10 mg/kg, s.c.) or AMT (1.0 mg/kg and 3.0 mg/kg, s.c.). Finally exposure to 50% N₂O for 15 min significantly increased NOS activity in the cerebellum and corpus striatum but not in other brain regions or whole brain. Conclusion. These findings provide further support for the hypothesis that NO is involved in N₂O-induced anxiolytic-like behavior and that this NO is the product of nNOS enzyme activity. Electronic Publication     

Functional response of the rat kidney to inhibition of nitric oxide synthesis: role of cytochrome P450-derived arachidonate metabolites

1. We tested the hypothesis that nitric oxide (NO) exerts a tonic inhibitory influence on cytochrome P450 (CYP450)-dependent metabolism of arachidonic acid (AA).
2. N^ω-nitro-L-Arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), increased mean blood pressure (MBP), from 91±6 to 137±5 mmHg, renal vascular resistance (RVR), from 9.9±0.6 to 27.4±2.5 mmHg ml⁻¹ min⁻¹, and reduced renal blood flow (RBF), from 9.8±0.7 to 6.5±0.6 ml min⁻¹) and GFR from 1.2±0.2 to 0.6±0.2 ml 100 g⁻¹ min⁻¹) accompanied by diuresis (UV, 1.7±0.3 to 4.3±0.8 μl 100 g⁻¹ min⁻¹), and natriuresis (U_NaV, 0.36±0.04 to 1.25±0.032 μmol 100 g⁻¹ min⁻¹).
3. 12, 12 dibromododec-enoic acid (DBDD), an inhibitor of ω hydroxylase, blunted L-NAME-induced changes in MBP, RVR, UV and U_NaV by 63±8, 70±5, 45±8 and 42±9%, respectively, and fully reversed the reduction in GFR by L-NAME. Clotrimazole, an inhibitor of the epoxygenase pathway of CYP450-dependent AA metabolism, was without effect.
4. BMS182874 (5-dimethylamino)-N-(3,4-dimethyl-5-isoxazolyl)-1-naphthalenesulfonamide), an endothelin (ET)_A receptor antagonist, also blunted the increases in MBP and RVR and the diuresis/natriuresis elicited by L-NAME without affecting GFR.
5. Indomethacin blunted L-NAME-induced increases in RVR, UV and U_NaV. BMS180291 (1S-(1α,2α,3α.4α)]-2-[[3-[4-[(pentylamino)carbonyl]-2-oxazolyl] - 7 - oxabicyclo[2.2.1]hept - 2 -yl]methyl]benzenepropanoic acid), an endoperoxide receptor antagonist, attenuated the pressor and renal haemodynamic but not the renal tubular effects of L-NAME.
6. In conclusion, the renal functional effects of the CYP450-derived mediator(s) expressed after inhibition of NOS with L-NAME were prevented by inhibiting either CYP450 ω hydroxylase or cyclo-oxygenase or by antagonizing either ET_A or endoperoxide receptors. 20-hydroxyeicosatetraenoic acid (20-HETE) fulfils the salient properties of this mediator.

     

Phosphodiesterase inhibition by sildenafil citrate attenuates a maze learning impairment in rats induced by nitric oxide synthase inhibition

Rationale The nitric oxide (NO)–cyclic guanosine monophosphate (cGMP) signal transduction pathway has been implicated in some forms of learning and memory. Recent findings suggest that inhibition of phosphodiesterase (PDE) enzymes that degrade cGMP may have memory-enhancing effects. Objectives We examined whether treatment with sildenafil citrate, a PDE type 5 inhibitor, would attenuate a learning impairment induced by inhibition of NO synthase [60 mg/kg N ^ω-nitro-l-arginine methyl ester (l-NAME), i.p.]. Methods Rats were pretrained in a one-way active avoidance of foot shock in a straight runway and, on the next day, received 15 training trials in a 14-unit T-maze, a task that has been shown to be sensitive to aging and impairment of central NO signaling systems. Combined treatments of l-NAME or saline and sildenafil (1.0, 1.5, 3.0, or 4.5 mg/kg, i.p.) or vehicle were given 30 and 15 min before training, respectively. Behavioral measures of performance included entries into incorrect maze sections (errors), run time from start to goal (latency), shock frequency, and shock duration. Results Statistical analysis revealed that l-NAME impaired maze performance and that sildenafil (1.5 mg/kg) significantly attenuated this impairment. Control experiments revealed that administration of l-NAME alone did not significantly increase latencies in a one-way active avoidance test and that different doses of sildenafil alone did not significantly alter complex maze performance. Conclusions The results indicate that sildenafil may improve learning by modulating NO–cGMP signal transduction, a pathway implicated in age-related cognitive decline and neurodegenerative disease. M. Jimenez and D. Sierra-Mercado, Jr., were supported by Minority Access to Research Careers grants NIGMS 08253 and NIGMS 07717.     

Effects of the nitric oxide donor,DEA/NO on cortical spreading depression

Cortical spreading depression (CSD) is a transient disruption of local ionic homeostasis that may promote migraine attacks and the progression of stroke lesions. We reported previously that the local inhibition of nitric oxide (NO) synthesis with Nomega-nitro-L-arginine methyl ester (L-NAME) delayed markedly the initiation of the recovery of ionic homeostasis from CSD. Here we describe a novel method for selective, controlled generation of exogenous NO in a functioning brain region. It is based on microdialysis perfusion of the NO donor, 2-(N,N-diethylamino)-diazenolate-2-oxide (DEA/NO). As DEA/NO does not generate NO at alkaline pH, and as the brain has a strong acid-base buffering capacity, DEA/NO was perfused in a medium adjusted at alkaline (but unbuffered) pH. Without DEA/NO, such a microdialysis perfusion medium did not alter CSD. DEA/NO (1, 10 and 100 microM) had little effect on CSD by itself, but it reversed in a concentration-dependent manner the effects of NOS inhibition by 1 mM L-NAME. These data demonstrate that increased formation of endogenous NO associated with CSD is critical for subsequent, rapid recovery of cellular ionic homeostasis. In this case, the molecular targets for NO may be located either on brain cells to suppress mechanisms directly involved in CSD genesis, or on local blood vessels to couple flow to the increased energy demand associated with CSD.     

Role of nitric oxide in allergic inflammation and bronchial hyperresponsiveness

The role of nitric oxide (NO) in allergic inflammation and bronchial hyperresponsiveness is unclear. We studied a selective prodrug nitric oxide synthase (NOS)-2 inhibitor, L-N(6)-(1-iminoethyl)lysine 5-tetrazole amide (SC-51). In ovalbumin-sensitized and challenged rats, exhaled NO levels increased by 3 h following challenge (3.73 +/- 0.74 ppb; P < 0.05), peaking at 9 h (11.0 +/- 2.75; P < 0.01) compared to saline controls (1.87 +/- 0.26; P < 0.05 and 2.81 +/- 0.18; P < 0.01). Immunoreactive lung NOS2 expression was increased in ovalbumin-challenged rats compared with ovalbumin-sensitized, saline-challenged rats at 8 h post-challenge. SC-51 (10 mg/kg; p.o.) inhibited allergen-induced increase in exhaled NO levels to 1.3 +/- 0.17 ppb. SC-51 inhibited bronchial hyperresponsiveness in ovalbumin-sensitized and challenged rats (P < 0.05). In sensitized non-exposed rats, SC-51 increased bronchial responsiveness (P < 0.05). SC-51 reduced the allergen-induced increase in bronchoalveolar lavage neutrophils, but caused a nonsignificant reduction in bronchial mucosal eosinophil numbers. NO generated through NOS2 contributes to allergen-induced bronchial hyperresponsiveness but not to bronchial eosinophilia, indicating that these are independently expressed.